I wish we hade some more info about the trading system, and the importance of roads.
Speculation is fun, so... let's speculate.
Let's assume, based on the current sketchy information, that ancient roads are generated by trade, and let's also assume we still control trade (at least the trade routes FROM our civilization to others).Then:
-We will still be able to decide which cities are connected by sending a trade route there.
-We have no control over the layout of such roads.
-Roads from our cities to city states and other Civs will be more common in Civ VI
-Other Civs will be able to create a road directly to our front door
(see image, roads underlined in yellow)
Also, if we look at the screenshots, it seems:
-Districts and wonders are always connected to the main city by roads.
Whether they are created automatically without a trade route, or they appear when the first trade route is established (and reflect how traders now "move" within our city) is anyone's guess at this time.
(see image, roads underlined in red, districts circled in blue)